Get rid of jagged shadow termination with sun lamp?

I have the following problem: I’m using a sky world texture plus a sun lamp to light my scene. The shadow termination on my smooth objects isn’t smooth, but faceted. This produces ugly shading artifacts in given angles (grazing angles to the sun direction).
This looks even worse with materials with a shader with textures normals.
See the picture + blend file, the right cube has a simple diffuse material, the left one has a procedural texture for a normal map.

How can I make the shadow termination smooth across the surface with a sun lamp? Without generating more geometry with subdivision.


smooth_surface_bug.blend (573 KB)

You can’t. At least not using Cycles. You will need to find a render engine that has solved the terminator issue. This is Thea, for example (pricey, though):